The technology shown in FIG. 12 has been known as such a fine bubble generating device (see, for example, Patent Literature 1). In this fine bubble generating device 100 consisting of a container body 102 with a conical space 101 that is closed on one end with a wall and open on the other end, a gas introducing bore 103 formed on the wall on the one end, and a pressurized liquid introducing inlet 104 formed on a part of an inner wall circumferential surface of the conical space 101 in a tangential direction thereof, the wall on the one end is comprised of a conical or truncated conical shaped part which protrudes out toward the other end, such that the longitudinal cross-sectional shape of the space on the one end has an M shape, and a swirling gas-liquid mixture solution including fine bubbles is drawn out from a swirling gas-liquid drawing outlet 105 of the cylindrical space 101 on the other end.
With the fine bubble generating device 100, a swirl flow is formed from the inlet (pressurized liquid introducing inlet) 104 toward the outlet (swirling gas-liquid drawing outlet) 105 by providing the conical space 101 in a device container. The swirl flow rate and the flow rate towards the outlet simultaneously increase at locations closer to the swirling gas-liquid drawing outlet 105 in accordance with the tapered shape of the conical space 101. By the generation of differences in swirl rates, a strand-like gas whirling tube section 106 is continuously and stably severed, resulting in generation of a large quantity of fine bubbles.